A turbocompressor, an expander or a positive displacement compressor, for example, is understood by a turbomachine. The turbocompressor has a casing and a rotor which is accommodated in the casing. The rotor has a shaft which is supported by its longitudinal ends outside the casing. As a result, the shaft passes through the casing by its longitudinal ends, wherein the shaft is sealed there against the casing by a shaft seal. Therefore, the interior of the turbocompressor is isolated from the atmosphere. The construction of the shaft seal is conventionally such that an arrangement is made first of all for a gas separator and then for an oil separator, as seen from the interior of the turbocompressor. The interior of the turbocompressor, that is to say the process side, is isolated by means of the shaft seal from the atmosphere and by means of the oil separator from the bearing region. The shaft seal is constructed as a gas-lubricated mechanical seal, for example, which is designed as a tandem seal. The tandem seal is constructed from two gas-lubricated mechanical seals which in each case have a sliding ring, which is fastened on the casing, and a counter ring, which is fastened on the shaft. Each sliding ring is arranged axially directly adjacent to its associated counter ring, forming an axial gap. The rings are arranged in the tandem seal in such a way that by the primary seal the process side is sealed against a flare pressure. By the secondary seal, the isolation against the atmosphere is brought about, wherein the secondary seal is provided additionally as redundancy to the primary seal in the event of failure of said primary seal. Barrier gas, which is used for blocking the axial gaps, is introduced between the two counter rings. In order to isolate the bearing region, a tertiary seal, for example, which can be constructed as a labyrinth seal or a carbon ring seal, is provided as the oil separator. The tertiary seal is acted upon by a barrier gas, as a result of which its blocking is brought about.